Osteoporosis is developed as a result of an imbalance between functions of osteoblasts, which play a role in osteogenesis, and osteoclasts, which play a role in deossification. Compounds that activate osteoblasts and compounds that suppress osteoclasts are considered to be effective in treating osteoporosis. Compounds having a single function, however, cannot produce satisfactory effects. Estrogen is deduced to activate osteoblasts and to suppress osteoclasts, and it is utilized in treating osteoporosis. Since estrogen also affects cells other than bones, particularly reproductive organs, side effects, such as increased risk of uterine cancer or breast cancer, may become an issue of concern. Also, the Ministry of Health, Labour and Welfare (Japan) issued safety information as of Jan. 29, 2004, to warn of the possibility of an increase in the development of breast cancer or dementia due to the prolonged ingestion of estrogen. Since estrogen has a complicated molecular structure, synthesis thereof is complicated and difficult.
Melatonin (N-acetyl-5-methoxytryptamine), which is an indole derivative represented by formula (I), is reported to act suppressively both on osteoblasts and osteoclasts:
wherein X represents a hydrogen atom; R1 represents a hydrogen atom; R2 represents methyl; R3, R5, and R6 each represent a hydrogen atom; and R4 represents methyl (N. Suzuki and A. Hattori, J. Pineal Res., 33, 253-258, 2002).
Also, it is reported that a compound represented by formula (I) wherein X represents a bromine atom; R1 represents a hydrogen atom; R2 represents methyl; R3, R5, and R6 each represent a hydrogen atom; and R4 represents methyl; a compound represented by formula (I) wherein X and R5 each represent a bromine atom; R1 represents a hydrogen atom; R2 represents methyl; R3 and R6 each represent a hydrogen atom; and R4 represents methyl; a compound represented by formula (I) wherein X and R3 each represent a bromine atom; R1 represents a hydrogen atom; R2 represents methyl; R5 and R6 each represent a hydrogen atom; and R4 represents methyl; and a compound represented by formula (I) wherein X, R3, and R5 each represent a bromine atom; R1 represents a hydrogen atom; R2 represents methyl; R6 represents a hydrogen atom; and R4 represents methyl can be obtained by brominating melatonin, although influences thereof on osteoblasts and osteoclasts have not been examined (M. Somei, Y. Fukui, M. Hasegawa, N. Oshikiri, and T. Hayashi, Heterocycles, 53, 1725-1736, 2000).